Leonardoxa africana (Baill.) Aubrév. subsp. africana (Baill.) Aubrev.

Mckey, Doyle B., 2000, Leonardoxa africana (Leguminosae: Caesalpinioideae): a complex of mostly allopatric subspecies, Adansonia (3) 22 (1), pp. 71-109 : 96-99

1. Leonardoxa africana (Baill.) Aubrév. subsp. africana (= group 4)

Tree to 14 m tall. Trunk (rarely) to 40 cm diam., usually under 15 cm diam. Young shoots produced in flushes consisting of only a single internode and young leaf at each branch tip. Internodes of young twigs (2.5-)3.5-7.5(-9) cm long, modified as myrmecodomatia, swollen, with thick pith except at base; twigs 4.3-5.7 mm diam. at apex tapering to ca. 2 mm diam. at base of internode; ant-cavities each a single internode long. Swollen internodes present from the seedling stage (20 cm tall) onward. Prostoma of ant-domatia at apex of internode opposite leaf insertion, elliptic. Leaves (2-)3(-rarely 4)-jugate. Leaflets elliptic, falcate, apex long-acuminate, the smallest leaflets (proximal pair) (7.8-)13(-15) cm long and (3.5-)5(-6) cm broad, the largest ones (distal pair in 2-jugate leaves, next-to-distal pair in 3- and 4-jugate leaves) (9.5-)15(-20) cm long and (4-)5.5(-7) cm broad; nectary glands large (smooth gland surface oblong, about 1 × 0.75 mm, surrounded by a raised ring of tissue about 1mm broad), consistently present on abaxial surface of each leaflet, with (2-)3-5 glands on each proximal leaflet, (1-)2(-3) glands on each median leaflet, and (0-)1-2 glands on each distal leaflet. Racemes to 4 cm long, with 40-50 flowers, usually cauliflorous, borne on main trunk and on large branches, or ramiflorous on twigs of ca. 5 mm diam. and larger. Flowers 1.8-2.2 cm in diam.; pedicels 2-4 mm long; calyx green or red, sepals 0.5-0.8 cm long; petals violet, purple, mauve, pink or red, 0.6-1.0 cm long. Ovules 4-5. Fruit oblongobovate, 8-11 cm long, 2.5-4 cm broad.

Leonardoxa africana subsp. africana is a highly specialised myrmecophyte, differing from the other myrmecophytic subspecies in a number of traits: (1) Foliar nectaries ( Fig. 5C ) are larger, more numerous, and less variable in presence/absence and number than in the other subspecies; (2) only a single leaf-bearing internode is produced in each flush of growth at a branch tip, so that each ant-cavity is a single internode long ( Figs. 6B , 7B ); (3) growth of different branch tips is not synchronised over the crown of the tree; (4) specialised swollen internodes appear much earlier (seedlings 20 cm tall) in plant ontogeny than in the other subspecies; (5) the prostoma is elliptic-oblong rather than spherical in shape ( Fig. 6D ). Also, while cauliflory on old branches, or even on the trunk, occurs in all three myrmecophytic subspecies, it appears to be especially frequent in subsp. africana ( Fig. 8B ).

DISTRIBUTION. — Leonardoxa africana subsp. africana is restricted to coastal forests of Cameroon ( Figs. 3 , 4 ). All the field sites are below 80 m elevation. Judging from collection localities and notes on labels, this subspecies appears rarely to occur above about 100 m. The northernmost known localities are from the Southern Bakundu Forest Reserve , and the southern boundary of its range appears to be near Campo , at the border with Equatorial Guinea. Within this coastal strip, it extends inland as far as Bipindi, on the eastern edge of the coastal plain.

ECOLOGY. — This subspecies, illustrated in AUBRÉVILLE (1970), is the one that has attracted most attention as a myrmecophyte. The studies by ELIAS (1980), MCKEY (1984), GAUME et al. (1997) and GAUME & MCKEY (1999) all concern this subspecies. Internodes are swollen and hollow, and these ant-domatia are present already in seedlings 20 cm tall (see Fig. 2B in LÉONARD [1993]). This subspecies is associated with two ant species that are completely restricted to this host, the formicine Petalomyrmex phylax and the myrmicine Cataulacus mckeyi ( MCKEY 1984) . Petalomyrmex is a mutualist of the plant, protecting its young leaves against phytophagous insects ( GAUME et al. 1997), while Cataulacus is a parasite, providing no protection to the plant and excluding Petalomyrmex from plants it occupies ( GAUME & MCKEY 1999). This subspecies was termed “ L. africana taxon T4” by CHENUIL & MCKEY (1996).

Few observations of flower visitors have been made, but on a few occasions sunbirds were seen visiting the pink to red flowers, which in this subspecies at least seem to have a somewhat longtubular corolla, compared to flowers of the non-myrmecophytic subspecies (see below).

ADDITIONAL SPECIMENS EXAMINED. — CAMEROON, Southwest Province: Southern Bakundu Forest Reserve , E.W. Jones in Brenan 9499 ( K, P), FHI 29511 (K), 29672 (K), and 41007 (K); Southern Bakundu Forest Reserve, 1 km W Bombe Bakundu , Manning 1499 ( MO); Southern Bakundu Forest Reserve , near Kindonge Camp , Manning 1517 ( MO); Kumba (planted in forestry nursery), FHI 29369 ( K). Littoral Province: 24 km E Douala, Breteler et al. 2580 ( BR, K, P, YA); Douala, route Razel , Endengle 2105 ( P, YA); Douala, forêt de Yelfoume , Fleury , in herb. Chevalier 33346 ( P); 14 km E Douala, Douala-Edea Road , Mpom 303 in part ( BR); Lake Tissongo, Douala-Edea Forest Reserve , McKey & Gartlan 120 ( K), D.W. Thomas 167 ( YA), Waterman & McKey 846 ( K); stream Mangombe near Edea , Mpom 343 ( YA). Central-South Province: near Bipaga II , km 40 from Kribi to Edea , de Kruif 994 ( WAG); Lolodorf Road, 12 km E of Kribi , Bos 3630 ( BR, WAG, YA); 5 km N of Lolodorf road, 19 km E of Kribi , Bos 3913 ( BR, YA); Lolodorf Road, 18 km E of Kribi , Bos 4074 ( BR, YA); km 30 from Kribi to Ebolowa , Bos 6233 ( WAG); km 45 from Kribi to Campo , Bos 7315 ( BR); 60 km S of Edea , S of Mboke, 11 km E of km 58 from Edea to Kribi , Leeuwenberg 5500 ( BR, K, MO, P, WAG, YA); colline Nkoltsia, Villiers 775 ( P); near Bella, Letouzey 4140 ( P, YA); 2 km from Nkol-Bewa , Mpom 227 ( P, YA); Edoudouma , Mpom 283 ( YA); Bipindi, Farron 7181 ( BAS, P, YA), Zenker, s.n. ( BR, P), 52 ( WAG), 1074 ( K, MO, P, WAG), 2967 ( BR, K, WAG), 4183 ( BR, K, P), 4495 ( BR, K, MO).

Figures

Fig. 5. — Foliar nectaries of the Leonardoxa africana complex, all shown at the same scale: A, L. africana subsp. gracilicaulis (Zingui hill site); B, L. africana subsp. rumpiensis (Dikomé Balué site); C, L. africana subsp. africana (Akanga site). Nectaries of L. africana subsp. letouzeyi (not pictured) are similar in size to those of subsp. rumpiensis.

Fig. 6. — Internodes of the Leonardoxa africana complex, showing variation in specialisations for housing ants. Bar = 2 cm in all photos. A, apex of internode (note point of attachment of the paripinnately compound leaf) of L. africana subsp. gracilicaulis (Mbalmayo site), showing absence of swelling in this non-myrmecophytic subspecies; B, longitudinal section of internode of L. africana subsp. africana (Bombé Bakundu site) showing the strongly swollen ant-domatium, which in this subspecies is a single internode long.— C and D, prostoma of two myrmecophytic subspecies, located in both cases at the apex of the internode opposite the point of leaf insertion; the diagonally cut structure at the top of each photo is the leaf rachis: C, circular prostoma of L. africana subsp. letouzeyi (Rengo Rock site); prostoma of L. africana subsp. rumpiensis (not shown) is roughly similar in size and shape; D, elongate prostoma of L. africana subsp. africana (Bombé Bakundu site). Both are on internodes produced by plants growing in a greenhouse at the University of Miami, on cuttings uninhabited by ants. The structures are not holes, but are scars produced by the spontaneous drying of the unlignified prostoma in mature internodes.

Fig. 7. — Examples of variation in the unit of growth within the Leonardoxa africana complex. A, a branch tip of L. africana subsp. rumpiensis (Dikome Balue site) showing two recently matured internodes and leaves produced in a flush of growth; these leaves are bright green (shiny in this photograph) and distinct from the older mature leaf (dark green, not shiny) produced in a previous growth flush; arrow marks the base of this flush. Bar = 10 cm. B, a branch tip of L. africana subsp. africana (Bombe Bakundu site) showing the one-leaf and internode unit of growth typical of all populations of this subspecies. Bar = 2 cm.

Fig. 8. — Variation in floral traits within the Leonardoxa africana complex. Bar = 2 cm in both photos. A, inflorescence axillary on a young twig (vertical object just behind the inflorescence) in L. africana subsp. gracilicaulis (Mbalmayo site); hypanthium white, corolla and filaments of stamens lilac, anthers yellow. B, trunciflorous inflorescences in L. africana subsp. africana (Grand Zambi); hypanthium and corolla pink.

Fig. 3. — Geographic distribution of field localities of members of the Leonardoxa africana complex: L. africana subsp. gracilicaulis = Group 1; L. africana subsp. rumpiensis = Group 2; L. africana subsp. letouzeyi = Group 3; L. africana subsp. africana = Group 4.

Fig. 4. — Geographic distribution of herbarium collections of the Leonardoxa africana complex examined in this study: L. africana subsp. gracilicaulis = Group 1; L. africana subsp. rumpiensis = Group 2; L. africana subsp. letouzeyi = Group 3; L. africana subsp. africana = Group 4.

Fig. 2. — Representation of the contribution of different characters to the first three dimensions of the principal components analysis of field populations of the Leonardoxa africana complex.